There’s a lot of motorcycle clothing out there these days. Some garments claim they’ll protect you in a crash, but how do you know for sure? How can you separate the real gear from the fashion wear? The right materials are important, and impact protection is a no-brainer, but what about seams? In this article, we’ll take a closer look at seams as a way to determine if you’re investing in quality riding gear. We’ll concentrate on seams for textile garments, especially those used in making jeans, since that’s what we’ve been obsessing over lately.
Seams are an often overlooked detail in a garment, though they’re essential to holding any sewn product together. Usually what we notice about a piece of clothing is its outward appearance. Does it come in my favorite color? Will the inseam or sleeves be long enough/short enough to fit me? Does it look “safe” enough for my needs? These are all questions easily answered by reading the item’s product details on a hang tag or website. But just like you wouldn’t buy a motorcycle because the fenders are shiny, you shouldn’t invest in motorcycle gear based on looks alone. Your gear is an integrated system – it’s the primary layer that protects you from the road. If your seams can’t hold up under pressure, there’s no amount of Kevlar or thick leather that will protect you as it’s ripped off your body in a crash.
Fabric can be joined together in many ways, but with garments and other textile products, stitched seams are the most efficient way to get that done (a discussion of duct tape or staples to hold a seam together can be found elsewhere on the Internets). The job of a seam in a sewn product is to attach two or more pieces of fabric together through one or more kinds of stitch types. A stitch (a single turn or loop of thread) is a fundamental element of sewing and also comes in different types. Put enough stitches together in a row and you’ve got yourself a seam. A seam can be made up of multiple lines of stitching, and each line of stitching can be of the same type or a combination of different types, depending on its purpose.
In a seam, the thread is also an important consideration, but for now we’ll talk about seam types in a thread-agnostic way. A discussion of thread types is coming up in another post anyway, so there’s something for you to look forward to. Besides, there’s plenty to study about seams without even getting started on thread, especially if you geek out about gear the way we do. First, let’s talk about the three most important considerations in motorcycle apparel seams: burst strength, abrasion resistance, and seam bulk.
The burst strength of a seam tells you how quickly that garment will fall apart upon impact with a hard surface, like the ground. One way to determine burst strength is by stitching two pieces of fabric together, then measuring how much force it takes to pull them completely apart (the Grab Test). Seams in motorcycle apparel should have a high burst strength, similar to seams in a pair of coveralls you might wear on a construction job site. In both activities, there’s a risk of falling, which means a risk of impact.
Impact forces in a motorcycle crash can be extremely high when you hit the road, making burst strength an important consideration when investing in gear. To examine seams for burst strength, turn the garment inside out. How many lines of stitching hold a single seam together? Pull lightly on the fabric on either side of the seam. If you can see through the seam when doing that, don’t buy it. Seams achieve higher burst strength by using more lines of stitching and more stitches per inch to hold the fabric together. A seam with a single line of stitching is not going to protect you in a crash.
Pro Tip: Don’t get caught ripping garment seams apart when you’re in the store, or they’ll kick your ass out.
Abrasion resistance is the ability of a garment to stand up to the grinding and scraping it receives when rubbing against an abrasive material, like concrete. This is where motorcycle gear differs from work wear garments, as construction workers have less risk of abrasion should they fall on a job site. Imagine “exiting your motorcycle” in a common low side get off (lean over too far in a turn while going too fast and your bike suddenly disappears from under you), and then sliding on your butt or outer thigh across the pavement for dozens of yards. Not only does your fabric need to withstand the abrasion of sliding across the pavement, but your seams do, too. Think of it like scrubbing 40 grit sandpaper across the seam rather than pulling on the fabric. Seams that hide all or some of the stitching inside the garment are more abrasion resistant than seams that have all the stitching exposed on the outside of the garment. Seams with multiple lines of stitching are more abrasion resistant than seams with only one line of stitching. The extra stitching provides backup in case one set sands completely through.
This video shows an approximate amount of time it takes to abrade completely through a pair of non-motorcycling denim jeans, based on the European CE standard for testing abrasion resistance. The test results are similar for waxed cotton and other fashion fabrics that contain only cotton (or cotton and a small amount of spandex). These materials alone will not protect you in a crash.
Seam bulk (the thickness of a seam after it’s been stitched together) is more of an issue of comfort rather than safety. It doesn’t matter how safe a garment is if you never wear it because it’s uncomfortable. In pants designed for motorcycling, try on the garment and sit on a motorcycle, if you can. Pay special attention to the seams in the inner thigh and crotch area where you may come in contact with the seat or the gas tank. If a seam is too thick or scratchy in that area, you may find yourself leaving that expensive gear in the closet on your next ride.
Now let’s look at some seam types commonly used in sewn products and see how they stack up to our three needs.
Single Needle Lockstitch “Butterfly” Seams
This is just about the simplest, fastest seam you can sew. A single line of stitching holds two pieces of fabric together. Once that’s been stitched, the seam allowances are opened up and pressed flat away from the seam to resemble a butterfly. It’s often used in fashion leather and pants – especially on selvage jeans – to show off the finished edge of the fabric as it comes off the loom at the mill (AKA the selvage). If you’re wearing jeans right now, it’s likely that the outside leg seam is a single needle butterfly stitch. The seam is easily made on home sewing machines.
The good: Since there are only two pieces of fabric held together with a single line of stitching, it’s not too bulky which adds to wearer comfort.
The bad: From a burst strength and abrasion resistance perspective, it’s not so great. If you’re in an accident and find yourself sliding on the pavement, this seam will come apart very quickly, leaving nothing between you and the open road.
Flat Felled Seams
In a flat felled seam (AKA “felled seam”), the two pieces of fabric to be joined are folded in on each other and then top stitched (see the diagram below, because I can’t explain the folding without using my hands, and I need my hands to type this article). This fold creates a mechanical bond and hides the edges of the fabric to prevent fraying. Two or three lines of topstitching pass through all four layers to hold everything together.
You can make a faux flat felled seam on a regular home machine, but it takes a few passes to do so – stitch, trim, fold, top stitch, then top stitch again. In factories, it’s done in one quick operation using a specialty machine with twin (or triple) needles and a folder attachment. This is the iconic double top stitch seam that used to be very common in jeans construction. Seams with less bulk are more often used now, but you can still find it at the yoke and center back seam of some brands of jeans. It’s commonly used in the outseams of heavy duty work wear, where burst strength is more important than bulk. Felled seams also have a clean appearance inside the garment since no fabric edges are exposed.
The good: The folded fabric and double stitching makes this seam very hard to pull apart, so it rates high for burst strength.
The bad: The four layers of fabric create bulk (two fabric layers + two fold layers), which can be uncomfortable in areas that are tight or rub against the body. In terms of abrasion resistance, the threads of all stitch lines are exposed on the outside of the garment, so if they are sanded away in a slide, the folding alone won’t hold the fabric together.
Safety Stitch Seams
A safety stitch seam consists of two stitches: a straight chainstitch and an overlock stitch. The chainstitch, which normally sits 1/4″ to 3/8″ from the edge of the fabric, is the part of the seam that provides the most strength. By itself, it’s similar in burst strength to the single needle butterfly seam. But the safety stitch has an added overlock stitch, which loops around the edges of the fabric with three more threads, for a total of five. The primary purpose of the overlock is to prevent fraying of exposed edges of the fabric. It also holds the two pieces together, providing a second line of stitching as backup if the chainstitch fails.
Safety stitch seams are very common on jeans and pants now. For a factory, it’s an efficient way to join two pieces of fabric and secure the edges from fraying in one operation. You’ll almost never find this seam on leather because leather doesn’t fray (when’s the last time you saw a frayed cow)? A common home sewing machine won’t make this seam. A five thread serger or a specialized industrial machine is necessary.
The good: The seam allowance in a safety stitch is folded to one side, rather than butterflied open. That means there are three layers of fabric in the seam – a little more bulk than a single needle butterfly seam, but not usually enough to affect comfort. Both stitches are hidden inside the garment, not directly exposed to abrasion, which is good. There are two lines of stitching, which is better than having just one.
The bad: Although there are two lines of stitching, one of them is a relatively weak overlock stitch. It’s not as strong as a flat felled seam in terms of burst strength. If you see this seam used in motorcycle apparel, make sure it’s reinforced with additional stitching, as in our next example.
Safety Stitch with Top stitching
Since the seam allowances are folded to one side in a safety stitch seam, it’s possible to add one or more lines of topstitching through the seam allowances and one side of the outer fabric. The extra stitches improve strength and abrasion resistance. With double topstitching, you have four stitches holding the seam together. The two topstitches are visible and exposed to abrasion, but the inner chainstitch and overlock are protected. There are still three layers of fabric like the safety stitch seam.
The good: This is a great seam for strength and abrasion resistance without being too bulky. The added top stitching provides additional reinforcement and comfort, since it holds the seam allowances tight to the fabric and prevents it from rubbing against your body.
The bad: It’s not so much bad for you as it is for the manufacturer. This seam is more rarely used because it takes longer to create. Two different machines are required – one for the safety stitch and one for the top stitching. That means two operations are necessary in the factory, instead of just one used in the other seam types we’ve discussed.
If topstitching both the inseam and outseam of pants, there’s also the additional challenge of topstitching up the leg after it’s fully assembled. The extra time and labor means you’ll rarely see this seam applied to both the inseam and outseam. If you do find a pair of pants with this feature, grab them. They’re worth the investment.
The cotton denim (non-motorcycling) jeans I wear most days have a single topstitched safety stitch seam on the inseam and a simple butterfly seam on the outseam. Again, because leather doesn’t fray, you’ll rarely find this seam on leather riding gear. However, you will see a very similar seam on good leather riding gear that omits the overlock, leaving one hidden and two exposed stitches. For textiles, the overlock prevents fraying and adds a one last backup stitch if all the other stitches fail.
There are a million things to think about when you’re buying gear – fit, function, price, durability, just to name a few. When you find something that looks good and seems well made, take the time to examine the seams. They’ll tell you a lot about the garment’s quality, and whether the manufacturer is compromising your safety just to save them a little time and money. Life is full of compromises, of course, and we’ve all worn something a little less than safe because it looked so good. It’s important to know when you’re compromising, though, so that you can make the decision for yourself.
Note: If you want to learn more about all types of seams, check out this handy seam and stitch type reference at garmento.org.